A hybrid vehicle is well known that includes an engine and an electric motor as a drive power source for running, an engine connecting/disconnecting clutch connecting/disconnecting a power transmission path between the engine and the electric motor, and an automatic transmission coupled to the electric motor side to transmit power from the drive power source for running toward drive wheels. For example, this corresponds to hybrid vehicles described in Patent Documents 1 to 3. Such a hybrid vehicle can generally perform motor running using only the electric motor as the drive power source for running with the engine connecting/disconnecting clutch released. During the motor running, a request for switching to engine running (hybrid running) including the engine as the drive power source for running may be made along with a shift request for the automatic transmission. Various control methods are proposed for start control of the engine and downshift control of the automatic transmission provided in such a case.
For example, Patent Document 1 describes an engine start method for a hybrid drive device in which if a start request for an engine and a downshift request for an automatic transmission are made because an operation of additionally depressing an accelerator pedal is performed during motor running, a downshift of the automatic transmission is first started before starting the engine while enjoying an improvement in acceleration due to kickdown. Patent Document 2 describes a control device of a hybrid vehicle in which if a start request for an engine and a downshift request for an automatic transmission are made during motor running, the engine is first started before providing shift control. Patent Document 3 describes a control device of a hybrid vehicle in which if an accelerator opening degree becomes equal to or greater than a predetermined degree during motor running, an engine is started during downshift of a transmission with the transmission put into a neutral state during the engine start.